When plated steel plate, for example galvanized plate, is painted while being transported on a belt conveyor it has not been possible to measure the quantity of paint, namely the thickness of paint, applied to the plated steel plate. In order to measure the thickness of the paint on the plated steel plate it has been the practice to stop the conveyor or remove the painted steel plate from the conveyor and measure the thickness of the paint by cutting a dry portion of the paint.
However, it has not been possible to measure the thickness of the paint applied as the steel plate is transported by the conveyor so as to be able to control the quantity of paint being applied to the plate.
It is an object of the present invention to provide a method and apparatus for measuring the thickness of paint on plated steel plate which is painted as it is being transported by a conveyor so as to be able to control the quantity of paint being applied by means of control apparatus, receiving a detecting signal which is detected as the thickness of the paint on the plated steel plate as it is being carried by the conveyor.
The method and apparatus in accordance with the invention are likewise applicable for measuring the thickness of other non-metallic layers, such as wood, polyvinyl or the like, which serve as a membrane coating deposited on the plated metal plate.
In accordance with the invention the thickness of the paint or other coating on the plated steel plate is measured by directing X-rays against the painted steel plate so as to produce fluorescent X-rays emitted from the plating layer and fluorescent X-rays emitted from the base plate, measuring the intensity of the fluorescent X-rays emitted from the plating layer and the intensity of the fluorescent X-rays emitted from the base plate and deriving the thickness of the paint or other coating from these intensities.
Apparatus for carrying out the method of the present invention accordingly comprises an exciting ray source for producing fluorescent X-rays emitted from the plating metal and from the base metal, a detector for detecting the emitted fluorescent X-rays and means for analyzing said X-rays and computing therefrom the thickness of the paint or other coating.
The nature, objects and advantages of the invention will readily be appreciated from the following description when considered in conjunction with the accompanying drawings.